
\begin{tikzpicture}[scale=.6]
  \coordinate (O) at (0,0);
  \coordinate[label=right:$A$] (A) at (6,0);
  \coordinate[label=above:$B$] (B) at (1,4);
  \coordinate[label=below:$A'$] (A') at ($ (O)!1! -90:(A) $);
  \coordinate[label=above:$B'$] (B') at ($ (O)!1! 90:(B) $);
  \coordinate[label=above right:$P$] (P) at ($ (A)!(O)!(B) $);
  \coordinate[label=left:$Q$] (Q) at ($ (A')!1/2!(B') $);
  \pic[mark angle={green}{3mm}{1}] {right angle=A'--O--A};
  \pic[mark angle={green}{3mm}{1}] {right angle=B--O--B'};
  \pic[mark angle={cyan}{3mm}{1}] {right angle=O--P--A};
  \node[below right] at (O) {$O$};
  \draw (O) -- (A) -- (B) -- (O) (O) -- (A') -- (B') -- (O) (P) -- (Q);
  \draw[blue] (A') -- (B');
\end{tikzpicture}
